printf format question

I know I'm mising something totally basic and obvious, but what format
specifier should I use when printing a variable of type clock_t ?

On amd64, a clock_t is typedef'd to "unsigned int" and printf %u works
fine. But on i386, clock_t is typedef'd to "unsigned long" and requires
printf %lu, and both %u and %llu fail to compile. There doesn't seem to
be any entry in i386/int_fmtio.h that equates to %lu